This invention concerns a method for the continuous casting of high-carbon steels.
By high-carbon steels are meant steels with a carbon content greater than 0.50%.
The method of this invention is applied to the field of the production by continuous casting of thin slabs of special steels having high mechanical and technological properties.
By thin slabs are meant slabs with a thickness less than 90 to 95 mm. and a width between 800 and 2500 to 3000 mm.
The method according to the invention has the purpose of perfecting the structural and technological characteristics with a view to adapting the continuous casting machine to the metallurgical properties which such special steels possess.
High-carbon steels, which are defined as steels having a carbon content of at least 0.50%, possess some metallurgical characteristics which are derived specifically from their composition and which make very delicate the continuous casting process if it is desired to obtain satisfactory qualitative results.
Such high-carbon steels, contrary to low-carbon steels such as peritectic steels for instance, are characterised by a low tendency towards shrinkage and contraction during their solidification step.
These high-carbon steels therefore do not entail problems of formation of depressions or of separation from the copper walls of the mould.
On the contrary, they are characterised by a strong tendency towards adherence, that is to say, adherence between the solidifying skin and the copper walls of the mould; this adherence leads to the stoppage of the casting process.
Moreover, such steels have a high speed of solidification in the mould, and this situation can cause wedge-shaped formations in the casting chamber of the mould if the transient state of start-up of the casting is carried out too slowly.
The article "Gallatin Steel follow thin slab route" in the Trade Journal "Iron and Steel International" of 1994 states clearly on page 55 and the following pages that no one has so far been able to cast high-carbon steels continuously; the table given on page 57 also shows clearly the absence of such types of steels with a carbon content greater than 0.50%.
At the Conference held in Peking in September 1993 a report entitled "Near-Net-Shape-Casting" was presented which was shown on page 391 and the following pages of the documents of the Conference.
That report indicates what was confirmed thereafter in the aforesaid article in the "Iron and Steel International".
This shows that technicians have been seeking for a long time a method suitable to cast continuously, and advantageously in the form of thin slabs, high-carbon steels, but without yet having succeeded.